The present invention relates to a new and useful apparatus and process for the operation of turbocompressors in which the throughput or a signal derived from the throughput and the discharge pressure or the pressure ratio, are continuously monitored and compared with permissible values. Measures are taken, according to the invention, to prevent surging. Upon reaching a blow-off line of the compressor characteristic curve which runs parallel to the surge limit, one or a plurality of blow-off valves are opened, for example, so that the compressor throughput does not fall below a minimum value which depends on the pressure ratio.
Surge limit control for compressors have already been undertaken with the use of mechanical/hydraulic controls. Despite high instrument and engineering expenditures, however, it is not possible in known controls to exactly adjust the blow-off line in order to reliably prevent surging. A further disadvantage lies in the high maintenance expense and the considerable susceptibility of these mechanical hydraulic control devices to trouble.
It is also known that an electronic surge limit control may be used for compressors (see Mitteilung 542 der Warmestelle des Vereins deutscher Eisenhutterleute, Report 542 of the Thermal Section of the German Ironworkers' Association). The surge limit control on compressors with guide vane adjustments is, in these units, designed similar to that of compressors with throttle adjustment, while, of course, there is the difference that because of the non-linear surge limit curve, a function generator is provided for the formation of the command variables of the surge limit control.
It has proven to be a disadvantage in these known control devices, that under certain operating conditions, that is, in the case of manual control intervention and with strong pressure fluctuations, surging of the compressor cannot readily be prevented.
U.S. Pat. No. 4,139,328 to Kuper et al (German Offenlegungsschrift 2,623,899), is incorporated here by reference. This patent teaches that an electronic surge limit controller may be used to control the blow-off valves, in which the control difference for the controller, which depends upon the actual pressure and throughput values, is amplified in a non-linear manner such that the amplification is increased when the control difference becomes negative, that is, when the operating point of the compressor moves into the impermissible range on the other side of the blowoff line of the compressor characteristic. Moreover, in this unit, an extreme value selector is imposed on the control, which selector takes into consideration the greatest control deviation, namely, the actual control deviation or the difference between control output and manual control command.
In this functional control device, it is, to be sure, a disadvantage that the rate of variation of the actual value cannot be taken into consideration or that allowance cannot be made for whether the deviation from actual value becomes greater or smaller. In practice, this means that, regardless of operating status, the blow-off line remains constantly in service.